{{Short description|Laboratory equipment}} {{For|the medical condition causing cold fingers|Raynaud syndrome}}

[[Image:Sublimation_apparatus.svg|thumb| Cold finger used in sublimation. The raw product (6) is in the bottom of the outer tube (4) which is heated (7) while under vacuum (through side-arm 3). The sublimated material collects (5) on the cold finger proper, cooled by a coolant (blue) circulated through ports 1 and 2.]]

A '''cold finger''' is a piece of laboratory equipment that is used to generate a localized cold surface. It is named for its resemblance to a finger and is a type of cold trap. The device usually consists of a chamber that a coolant fluid (cold tap water, or perhaps something colder) can enter and leave. Another version involves filling the device with a cold material (examples: ice, dry ice or a mixture such as dry ice/acetone or ice/water).<ref>{{cite book|title=Laboratory Technique in Organic Chemistry|url=https://archive.org/details/laboratorytechni00wibe_0|url-access=registration|author=Kenneth B. Wiberg|isbn=0070700958|year=1960|publisher=McGraw-Hill}}</ref>

Typically a cold finger is used in a sublimation apparatus,<ref>{{Cite book|title=The Organic Chem Lab Survival Manual: A Student's Guide to Techniques|last=Zubrick|first=James W.|publisher=John Wiley & Sons|year=2016|isbn=978-1118875780|location=United States of America|pages=192–194|chapter=Sublimation|edition=10th }}</ref> or can be used as a compact version of a condenser in either reflux reaction or distillation apparatus. Many commercially available rotary evaporators can be purchased with a cold finger in place of a Dimroth condenser, for example. When used as a condenser in a rotary evaporator, cold fingers can be cooled to a lower temperature of &minus;78&nbsp;°C (dry ice), compared with water condensers that can be cooled to &minus;40&nbsp;°C (ethylene glycol/water mixture). The lower temperature achieved reduces the quantity of volatile material exhausted into the air.

==Media== <gallery widths="150px" heights="200px"> Image:Cold finger 1.jpg|A cold finger which includes a vacuum outlet. image:Camphor sublimation 1.jpg|Camphor being sublimed. The crude product in the bottom is dark brown; the white purified product on the bottom of the cold finger above is hard to see against the light background. image:Cp2NiSublimate.jpg|Dark green crystals of nickelocene, freshly sublimed on a cold finger. </gallery>

==References== {{reflist}}

{{Laboratory equipment}}

{{DEFAULTSORT:Cold Finger}} Category:Laboratory glassware